Junk food won"t just make you fat, it could also shrink your brain

Piling on the pounds damages our hearts, joints and arteries — this fact is well-established.

What is less well-known is that being obese, or even just overweight, can also damage our brains.

Not only can it alter the brain’s physical structure, triggering memory problems and an increased risk of dementia, but it can also prematurely age the grey matter — on average adding an extra 16 years.

Being overweight can change the way we think, affecting our judgment and making us crave even more high-calorie fodder

Grey matter is the ‘thinking part’ of the brain, and consists of brain cells involved in muscle control, seeing, hearing, memory, emotions, and speech.

The white matter is the ‘nerve motorway’ — the material that connects these cells to each other.

Being overweight can change the way we think, too, affecting our judgment and making us crave even more high-calorie fodder. As a result, we seek out a food ‘fix’ in the same way a drug addict needs narcotics.

With a quarter of adults and one in seven children in England thought to be obese — classified as having a Body Mass Index (BMI) of more than 30 — the implications are alarming.

Furthermore, it’s not just the obese who are affected — even being overweight is a problem for the brain (around 32 per cent of women and 42 per cent of men are overweight, with a BMI of more than 25).

‘The problem is we evolved over time to see sugary and fatty foods as appealing, because in periods of starvation or lack of food these would save us,’ says Dr Tony Goldstone, Consultant Endocrinologist at the Imperial College Healthcare NHS Trust.

‘Now they are now more available than ever, which is why we’ve become so fat.’

Just last month, researchers at the Karolinska Institute in Sweden declared the risk of dementia in later life is 71 per cent higher for overweight people, and around four times greater for those who were obese in middle age.

The problem, say scientists, is fat, as it causes the brain to shrink.

‘We know that a fatty diet clogs our arteries and is bad for our heart, and it does exactly the same thing to blood vessels in the brain,’ explains Paul Thompson, professor of neurology at the University of Los Angeles and an expert in this field.

Being overweight can prematurely age the grey matter – the “thinking part” of the brain

His team found the brains of overweight and obese subjects were, on average, between 4 and 8 per cent smaller than the brains of those who were at a healthy weight.

‘This is because blood can’t get through so easily to the brain — it’s starved of oxygen and the brain cells eventually die, he says.’

This has the effect of prematurely ageing the brain.

The researchers, who examined brain scans of nearly 100 people aged over 70, concluded the brains of overweight people were on average eight years older than those of their healthy counterparts.

‘We based this on the fact that the average person loses 0.5 per cent of their brain a year,’ says Professor Thompson.

‘The overweight people had already lost 4 per cent more than someone of a normal weight, so they were effectively eight years older.’

The news was worse for obese people: ‘They had lost 8 per cent of their brain, so they were 16 years older. It won’t kill you, but there will come a point when it’s noticeable — when about 10 per cent of your brain tissues have died,’ he adds.

And for the obese, there is more bad news: the scans also revealed the areas where the shrinkage was most pronounced were those responsible for reasoning and judgment and the processing of long-term memories.

Whether you’re obese or just overweight, the researchers believe a shrunken brain is less resilient to damage from the abnormal protein clumps in the brain called plaques that kill brain cells and cause Alzheimer’s.

‘It may be that you are building up plaques in the brain and then being obese tips you over the limit into having Alzheimer’s,’ says Professor Thompson.

To support this, other research has shown obese individuals have less grey matter and more white matter than people with healthy BMIs.

‘Obese people, or those who have a binge-eating disorder, may also have differences in the structure of some parts of the brain compared with their thinner counterparts,’ says Dr Goldstone.

‘Some studies have shown subtle differences in how dense and well organised the grey or white matter in the brain of obese people and those who are not.’

But could losing weight or having obesity surgery improve memory and cognitive functioning once again

The evidence emerging suggests it may well do, according to researchers at Kent State University, Ohio.

The memories of 150 overweight people were tested before some of the participants underwent gastric bypass surgery.

Around 12 weeks after surgery, those who’d had the operation showed improvements in memory, moving from a score of mildly impaired into the normal range. The improvements were not mirrored in the patients who didn’t have surgery.

Tests included the ability to recall words, problem solving and reaction times.

So what is causing the improvement in these people’s brains

‘Research has shown that when people gain weight they tend to have more problems learning and recalling new information, problem solving and co-ordination,’ says John Gunstad, associate professor in the department of psychology, who led the research.

‘It’s a really big challenge to work out why, but it’s thought the changes in blood pressure and glucose levels that accompany weight gain might also be to blame.

‘In addition, obese people are more likely to suffer from sleep apnoea, which affects concentration during waking hours.

‘There are a whole host of possible factors. What we do know is that losing weight seems to enable the brain to function normally again.’